Mass flow verification based on rate of pressure decay

ABSTRACT

An electronic device manufacturing system includes: a gas supply; a mass flow controller (MFC) coupled to the gas supply; an inlet coupled to the MFC; an outlet; a control volume serially coupled to the inlet to receive a gas flow; and a flow restrictor serially coupled to the control volume and the outlet. A controller is adapted to allow the gas supply to flow gas through the control volume and the flow restrictor to achieve a stable pressure in the control volume, terminate the gas flow from the gas supply, and measure a rate of pressure decay in the control volume over time. A process chamber is coupled to a flow path, which is coupled to the mass flow controller, the process chamber to receive one or more process chemistries via the mass flow controller.

RELATED APPLICATIONS

This is a divisional application of, and claims priority from, U.S.patent application Ser. No. 15/936,428, filed Mar. 26, 2018, andentitled “Methods, Systems, and Apparatus for Mass Flow VerificationBased on Rate of Pressure Decay,” the disclosure of which is herebyincorporated by this reference herein.

FIELD

This disclosure relates to electronic device manufacturing and, moreparticularly, to verifying mass flow rates of mass flow controllersbased on rate of pressure decay.

BACKGROUND

Electronic device manufacturing systems may include one or more massflow controllers (MFCs). MFCs control the mass flow rates of processchemistries used in the manufacture of electronic devices. Processchemistries may include various process gases (e.g., cleaning,deposition, and etchant gases) that are delivered to one or more processchambers in which electronic devices may be fabricated on semiconductorwafers, glass plates, or the like. Precise mass flow control of processgases may be used in one or more steps of an electronic device'sfabrication process. Precise mass flow control provided by MFCs maycontribute to high yield production of electronic devices havingmicroscopically small dimensions.

To ensure that process chemistries are delivered accurately,verification and calibration of MFC's may be performed periodically.However, conventional methods of verifying and calibrating MFCs mayinvolve significant additional bulky and expensive equipment that may betime consuming and inefficient to use, may be limited to low mass flowrate ranges (e.g., up to only 3000 seem (standard cubic centimeter perminute) nitrogen equivalent), may result in notable process downtime,and/or may not be sufficiently accurate to ensure precise mass flowcontrol of process chemistries.

SUMMARY

In some embodiments, an electronic device manufacturing system isprovided. The electronic device manufacturing system includes a gassupply; a mass flow controller (MFC) coupled to the gas supply; an inletcoupled to the MFC; an outlet; a control volume serially coupled to theinlet to receive a gas flow; and a flow restrictor serially coupled tothe control volume and the outlet. The system further includes acontroller adapted to allow the gas supply to flow gas through thecontrol volume and the flow restrictor to achieve a stable pressure inthe control volume, terminate the gas flow from the gas supply, andmeasure a rate of pressure decay in the control volume over time. Thesystem further includes a process chamber coupled to a flow path, whichis coupled to the mass flow controller, the process chamber to receiveone or more process chemistries via the mass flow controller

In some other embodiments, a method is disclosed of verifying a massflow controller. The method of verifying a mass flow controller includescausing a gas to flow from a gas supply through a calibrated flowstandard, a control volume, and a flow restrictor at a steady pressuremeasured in the control volume; terminating the gas flow from the gassupply; measuring a first rate of gas pressure decay in the controlvolume; replacing the calibrated flow standard with the mass flowcontroller; causing the gas to flow from the gas supply through the massflow controller, the control volume, and the flow restrictor at a stablepressure measured in the control volume; terminating the gas flow fromthe gas supply; and measuring a second rate of gas pressure decay in thecontrol volume for purposes of verifying the mass flow controller.

In yet other embodiments, a system is provided. The system includes aninlet coupled to a mass flow controller, which is coupled to a gassupply; an outlet; a control volume serially coupled to the inlet toreceive a gas flow; a flow restrictor serially coupled to the controlvolume and the outlet; and a controller adapted to allow the gas supplyto flow gas through the control volume and the flow restrictor toachieve a stable pressure in the control volume, terminate the gas flowfrom the gas supply, and measure a rate of pressure decay in the controlvolume over time to verify the mass flow controller.

Still other aspects, features, and advantages in accordance with theseand other embodiments of the disclosure may be readily apparent from thefollowing detailed description, the appended claims, and theaccompanying drawings. Accordingly, the drawings and descriptions hereinare to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

The drawings, described below, are for illustrative purposes only andare not necessarily drawn to scale. The drawings are not intended tolimit the scope of the disclosure in any way.

FIG. 1 illustrates a first mass flow control verification systemaccording to embodiments of the disclosure.

FIG. 2 illustrates a second mass flow control verification systemaccording to embodiments of the disclosure.

FIG. 3 illustrates a third mass flow control verification systemaccording to embodiments of the disclosure.

FIG. 4 illustrates a graph of several pressures measured during massflow verification according to embodiments of the disclosure.

FIG. 5 illustrates an electronic device manufacturing system accordingto embodiments of the disclosure.

FIG. 6 illustrates a flowchart of a method of mass flow controlverification according to embodiments of the disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments of thedisclosure, which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Electronic devices having microscopically small dimensions may beproduced with process gas chemistries having mass flow rate accuraciesas high as +/−1%. Many mass flow controllers (MFCs) may be specified assuch and may meet those specifications when new, while a smallpercentage of MFCs may be specified as such, but may not actually meetthem when new or otherwise. Furthermore, even initially accurate MFCsmay over time experience an accuracy drift in their mass flow rates thatmay render them outside of their specified accuracies. Accordingly,verification and calibration of MFCs, such as those used insemiconductor fabrication equipment, may be performed periodically toensure that process gas chemistries are delivered accurately.

Existing methods and the associated hardware for mass flow verificationtypically operate based on measuring pressure rate of rise (ROR) in aknown volume. ROR principles are based on the ideal gas law being usedto correlate a mass flow rate with a measured pressure rate of rise in aknown enclosed volume. The higher the mass flow rate, the larger theenclosed volume should be to ensure accuracy. ROR principles may involvea lengthy process (e.g., 10 or more hours in some cases) of filling anenclosed volume with a gas and measuring ROR within the enclosed volume.The enclosed volume may be a process chamber of a manufacturing systemor an external volume. Uncertainties in the exact volume of a processchamber or external volume may adversely affect the accuracy of theresults. A process using ROR principles may involve measurements ofpressure, temperature, volume, and time. One significant problem withconventional ROR-based methods is that the known volume typicallyincludes a reservoir and the flow path leading to the reservoir from theMFC unit under test (UUT). The rate of pressure change is measuredinside the reservoir at almost stagnation and the dynamic pressureinside the flow path leading to the reservoir is not measured. Lack ofthe measurement of rate of pressure change in one of the two portions ofthe known volume can result in erroneous calculations leading tomischaracterization of the flow out of the UUT. In contrast with suchconventional methods, embodiments disclosed herein eliminate the errorintroduced by the volume of the flow path. The present methods andapparatus operate based on measuring the rate of pressure decay in aknown volume and thus, does not include an unmeasured flow path.

More specifically, mass flow verification methods, systems, andapparatus in accordance with one or more embodiments of the disclosureare based on pressure decay principles for determining a gas mass flowrate, which may be in units of “seem” (standard cubic centimeters perminute) or “slm” (standard liters per minute). Mass flow verificationmethods, systems, and apparatus based on pressure decay principles inaccordance with one or more embodiments of the disclosure may reduce thenumber of variables needed to calculate mass flow rate, may result in asmaller verification equipment footprint, and may be more time efficientand more accurate than mass flow verification methods, systems, andapparatus based on conventional ROR-based principles. In contrast toROR-based methods, non-ROR pressure decay measurement may be almostinstantaneous, and calculating a mass flow rate based on rate ofpressure decay (ROPD) principles may involve just twomeasurements—pressure and temperature.

The ideal gas law, also called the general gas equation, is the equationof state of a hypothetical ideal gas. It is an approximation of thebehavior of many gases under many conditions. The ideal gas law is oftenexpressed as:(PV=nRT)where P is the pressure of the gas, V is the volume of the gas, n is theamount of substance of gas (in moles), R is the ideal, or universal gasconstant, equal to the product of the Boltzmann constant and theAvogadro constant, and T is the absolute temperature of the gas.

FIG. 1 depicts an example arrangement for verifying a MFC. The mass flowverification system 100 of FIG. 1 includes a gas supply 102 thatprovides a pressurized flow of a suitable gas (e.g., nitrogen, oxygen,clean dry air (CDA), etc.) to a location 104. The flow rate of the gasis unlimitedly scalable by specifying appropriate monitored volume 110and flow restrictor 116 sizes. At location 104, either a reference(e.g., a calibrated flow standard) or a UUT can be positioned to receivethe gas. The output of the reference or UUT at location 104 can becoupled to a line 106 leading to a valve 108 (e.g., an isolation valve)that is coupled to a monitored volume 110. The monitored volume 110 ismonitored using a connected thermocouple 112 and a connected manometer114 or other suitable pressure measuring device. The output of themonitored volume 110 is coupled to a flow restrictor 116 which iscoupled to a vacuum pump 118. In some embodiments, the flow restrictor116 can be a drilled orifice flow restrictor, or a porous media flowrestrictor when pressure and temperature downstream of the flowrestrictor 116 are measured. The mass flow verification system 100 isoperated under the control of controller 120 which can be coupled toeach operable component and each sensor component (n.b., connections arenot shown for illustrative clarity).

Using the arrangement shown in FIG. 1 , the Control Volume (V) (i.e.,the labeled volume between valve 108 and flow restrictor 116 includingmonitored volume 110) is first determined by using a calibrated flowstandard in location 104. The calibrated flow standard at location 104is given a set point and adequate time is allowed for pressure andtemperature in the monitored volume 110 to stabilize to a steady state.At time t_(o), where the pressure is measured and labeled P_(o), valve108 is commanded to be closed by controller 120. After time t_(o), thepressure inside the Control Volume begins to decay as the gas continuesto flow through the flow restrictor 116. The Control Volume iscalculated based on:V=RT(dn/dt)/(dP/dt)Evaluating dP/dt at t_(o) where the pressure is P_(o) and using the setpoint of the calibrated flow standard at location 104 as dn/dt at t_(o)in the above equation provides the value for the Control Volume. Oncethe volume of the Control Volume is determined, the calibrated flowstandard at location 104 is replaced with a UUT MFC. The UUT MFC isgiven a set point that is to be verified. Solving the above equation fordn/dt, the accuracy of the UUT MFC can be determined by comparing thegiven set point to the calculated mass flow rate using the equation:dn/dt=(V/RT)(dP/dt)

The above described method assumes that valve 108 closesinstantaneously. In reality, the actual time it takes for the completeclosure of valve 108 due to latencies in communication from thecontroller 120 and hardware actuator response is some small butsignificant amount Δt beyond t_(o). During Δt, the calibrated gas flowis still flowing into the Control Volume while pressure inside theControl Volume is decaying at a rate slower than indicated by the abovecalculations as a result of the latencies. Once valve 108 is completelyclosed, the calibrated gas flow no longer flows into the Control Volumeand the pressure inside the Control Volume continues to decay, but at afaster rate. Embodiments of the present disclosure provide methods andapparatus to compensate for the time Δt it takes for value 108 to closecompletely. Specifically, embodiments of the disclosure provide methodsfor evaluating dP/dt at t_(o) even though the mass flow rate is steadyonly after Δt has elapsed.

In the first example method of evaluating dP/dt at t_(o), using the massflow verification system 100 shown in FIG. 1 with a calibrated flowstandard installed at location 104 at a known set point, valve 108 isopened to establish flow through the control volume and pressure ismeasured in the monitored volume 110 via the manometer 114. Note thatthe valve 108 is normally closed until actuated. Enough time toestablish a steady state, stabilized flow is allowed to pass until abaseline measurement of P_(o) can be made. Referring to graph 400 ofFIG. 4 and specifically the changing pressure over time dP/dt plot 402,P_(o) is stabilized during the time before t_(o). At t_(o) valve 108 isclosed. Next, the time t_(o)+Δt is determined by locating the decayingpressure inflection point 404 on the dP/dt plot 402. Next, the measureddata points beyond time t_(o)+Δt are used to determine an equation forthe decaying pressure. Any number of curve fitting algorithms or methodscan be used to determine the equation of the curve. Next, based on thedetermined equation, the corrected value of dP/dt at P_(o) (i.e., point406) is extrapolated back from the measured data points. The correctedvalue of dP/dt at P_(o) for the calibrated flow standard is then used tocalculate V based on:V=RT(dn/dt)/(dP/dt)as described above. Next, a MFC UUT is installed at location 104 set ata test set point. Valve 108 is then opened to once again establish flowthrough the control volume and pressure is measured in the monitoredvolume 110 via the manometer 114. Enough time to establish a steadystate, stabilized flow is allowed to pass until a baseline measurementof P_(o) for the UUT can be made. Once P_(o) is stabilized during thetime before t_(o), valve 108 is closed establishing time t_(o) for theUUT. Next, the time t_(o)+Δt tis determined by locating the decayingpressure inflection point 404 on an equivalent of the dP/dt plot 402.Next, the measured data points beyond time t_(o)+Δt are used todetermine an equation for the decaying pressure. Any number of curvefitting algorithms or methods can be used to determine the equation ofthe curve. Next, based on the determined equation, the corrected valueof dP/dt at P_(o) for the UUT (i.e., point 406) is extrapolated from themeasured data points. The equation for actual mass flow is:dn/dt=(V/RT)/(dP/dt)Finally, using the above equation, the corrected value of dP/dt at P_(o)for the UUT is used to compute the actual mass flow (dn/dt) which iscompared to the test set point to determine any error. In someembodiments, based on the error, the UUT MFC can be calibrated tocorrect the error.

An alternative second example method for MFC verification can be used tofurther enhance the accuracy of the verification. The second method usesthe MFC verification system 200 depicted in FIG. 2 . The mass flowverification system 200 includes a gas supply 202 that provides apressurized flow of a suitable gas (e.g., nitrogen, oxygen, clean dryair (CDA), etc.) to a location 204. The flow rate of the gas isunlimitedly scalable by specifying appropriate monitored 210 volume andflow restrictor 216 sizes. At location 204, either a reference (e.g., acalibrated flow standard) or a UUT can be positioned to receive the gas.The output of the reference or UUT at location 204 can be coupled to aline 206 leading to a valve 208 (e.g., an isolation valve) that iscoupled to a monitored volume 210. The monitored volume 210 is monitoredusing a connected thermocouple 212 and a connected manometer 214. Theoutput of the monitored volume 210 is coupled to a second valve 222which is coupled to a flow restrictor 216. In some embodiments, the flowrestrictor 216 can be a drilled orifice restrictor, or a porous mediaflow restrictor when pressure and temperature downstream of the flowrestrictor 216 are measured. The output of the flow restrictor 216 iscoupled to a vacuum pump 218. The mass flow verification system 200 isoperated under the control of controller 220 which can be coupled toeach operable component and each sensor component (n.b., connections arenot shown for illustrative clarity).

Note that the MFC verification system 200 is structurally identical tothe MFC verification system 100 of FIG. 1 except that a second valve 222operated by controller 220 is disposed in the line between the monitoredvolume 210 and the flow restrictor 216. Use of the second valve 222allows the initial pressure in the Control Volume to be boosted up abovethe initial stabilized pressure as compared to the initial pressure usedin the first example method. By boosting the initial pressure before thedecay period begins, it is possible to take more pressure measurementsover a prolonged decay period and thereby have more data points to fit aconsequently more accurate curve from which to determine a more accuratecharacteristic equation. The boosted initial pressure is represented asP_(o)′ on the changing pressure over time dP/dt plot 408 in graph 400 ofFIG. 4 .

The alternative second example method for MFC verification includes thefollowing. Initially, both valve 208 and valve 222 are opened longenough to establish steady state stable flow and measure pressure. Thenvalve 222 is closed for a period of time sufficient to create a pressurerise in the Control Volume up to P_(o)′. Once P_(o)′ is reached, valve222 is opened simultaneously with valve 208 being closed. Next, the timet_(o)′+Δt is determined by locating the decaying pressure inflectionpoint 410 on the dP/dt plot 408. Next, the measured data points beyondtime t_(o)′+Δt are used to determine an equation for the decayingpressure. Any number of different curve fitting algorithms or methodscan be used to determine the equation of the curve. Next, based on thedetermined equation, the corrected value of dP/dt at P_(o)′ (i.e., point412) is extrapolated from the measured data points. The corrected valueof dP/dt at P_(o)′ for the calibrated flow standard is then used tocalculate V based on:V=RT(dn/dt)//(dP/dt)as described above. Next, a MFC UUT is installed at location 204 inplace of the reference, set at a test set point, and the above describedmethod is repeated to determine dP/dt at P_(o)′. The equation for actualmass flow is:d/dt=(V/RT)/(dP/dt)Finally, using the above equation, the corrected value of dP/dt atP_(o)′ for the UUT is used to compute the actual mass flow (dn/dt) whichis compared to the test set point to determine any error. In someembodiments, based on the error, the UUT MFC can be calibrated tocorrect the error.

An alternative third example method for MFC verification can be used tofurther enhance the accuracy of the verification. The third method usesthe MFC verification system 300 depicted in FIG. 3 . The mass flowverification system 300 includes a gas supply 302 that provides apressurized flow of a suitable gas (e.g., nitrogen, oxygen, clean dryair (CDA), etc.) to a location 304. The flow rate of the gas isunlimitedly scalable by specifying appropriate monitored volume 310 andflow restrictor 316 sizes. At location 304, either a reference (e.g., acalibrated flow standard) or a UUT can be positioned to receive the gas.The output of the reference or UUT at location 304 can be coupled to aline 306 leading to a valve 308 (e.g., an isolation valve) that iscoupled to a monitored volume 310. The monitored volume 310 is monitoredusing a connected thermocouple 312 and a connected manometer 314 orother suitable pressure sensor. The output of the monitored volume 310is coupled to a flow restrictor 316. In some embodiments, the flowrestrictor 316 can be a drilled orifice restrictor or a porous mediaflow restrictor when pressure and temperature downstream of the flowrestrictor 316 are measured. The output of the flow restrictor 316 iscoupled to a vacuum pump 318. The mass flow verification system 300 isoperated under the control of controller 320 which can be coupled toeach operable component and each sensor component (n.b., connections arenot shown for illustrative clarity). Also connected to line 306 (inparallel with valve 308) is a second valve 324 which is coupled to asecond volume 326. Second volume 326 includes an output coupled to athird valve 328 which has its output coupled to the monitored volume310.

Use of the second valve 324, the second volume 326, and the third valve328 allows the initial pressure in the Control Volume to be boosted upabove the initial stabilized pressure as compared to the initialpressure used in the first example method. A store of pressurized gas iscontained in the second volume 326 and injected into the monitoredvolume 310 to boost the initial pressure in the monitored volume 310before the decay period begins. As with the second example method, thisallows more pressure measurements to be made during a prolonged decayperiod (e.g., relative to the first example method) and thereby havemore data points to fit a consequently more accurate curve from which todetermine a more accurate characteristic equation. As with the secondexample method, the boosted initial pressure is represented as P_(o)′ onthe changing pressure over time dP/dt plot 408 in graph 400 of FIG. 4 .

The alternative third example method for MFC verification includes thefollowing. Initially, second valve 324 is opened to establish flow andpressurize second volume 326. Second volume 326 can be pressurized up tothe pressure level of the gas supply 302. In some embodiments,additional equipment (e.g., a pump) can be used to pressurize the secondvolume 326 to higher levels. Then the second valve 324 is closed and thefirst valve 308 is opened long enough to establish steady state stableflow and to measure pressure in the monitored volume 310. Once thebaseline P_(o) stabilized pressure is reached, the first valve 308 isclosed simultaneously with the third valve 328 being opened. The thirdvalve 328 is left open for a period of time sufficient to create apressure rise in the Control Volume up to P_(o)′. Once P_(o)′ isreached, third valve 328 is closed. Next, the time t_(o)′+Δt isdetermined by locating the decaying pressure inflection point 410 on thedP/dt plot 408. Next, the measured data points beyond time t_(o)+Δ areused to determine an equation for the decaying pressure. Any number ofdifferent curve fitting algorithms or methods can be used to determinethe equation of the curve. Next, based on the determined equation, thecorrected value of dP/dt at P_(o)′ (i.e., point 412) is extrapolatedback from the measured data points. The corrected value of dP/dt atP_(o)′ for the calibrated flow standard is then used to calculate Vbased on:V=RT(dn/dt)/(dP/dt)as described above. Next, a MFC UUT is installed at location 204 inplace of the reference, set at a test set point, and the above describedmethod is repeated to determine dP/dt at P_(o)′. The equation for actualmass flow is:dn/dt=(V/RT)(dP/dt)Finally, using the above equation, the corrected value of dP/dt atP_(o)′ for the UUT is used to compute the actual mass flow (dn/dt) whichis compared to the test set point to determine any error. In someembodiments, based on the error, the UUT MFC can be calibrated tocorrect the error.

Flow restrictors with particularly small diameter drilled orifices arechallenging to manufacture with tight reproducibility specifications.The present example methods and apparatus removes the variability of theflow restrictor out of the equation. In some embodiments, the presentexample methods and apparatus can be used to determine the dischargecoefficient of drilled orifices and to characterize porous media flowrestrictors by calculating the ratio of actual mass flow rate overtheoretically computed mass flow rate.

The use of the ideal gas equation as described above forreduced-pressure (i.e., vacuum-based) applications provides sufficientaccuracy for verification of reduced-pressure MFCs. In embodimentsadapted for atmospheric applications (e.g., without vacuum pumps) anon-ideal gas equation (such as the van der Waals equation below) can beapplied to the present methods and apparatus for mass flow verification.The van der Waals equation is given as:

${\left( {P + \frac{{an}^{2}}{V^{2}}} \right)\left( {V - {nb}} \right)} = {nRT}$and can be used in place of the ideal gas law for atmosphericapplications by applying gas specific corrections for intermolecularforces (parameter a) and for finite molecular size (parameter b) to theequation above. For wider range mass flow verification requirements,multiple volume sizes can be used. In these cases, a single optimizedvolume with appropriate partitions can be used. Partitions divide up thevolume into smaller segments and by selective removal of partitions,multiple combinations of larger volumes may be created.

FIG. 5 illustrates an electronic device manufacturing system 500 inaccordance with one or more embodiments. Electronic device manufacturingsystem 500 may include an MFC 502, a mass flow verification system 504,and a process chamber 506. In some embodiments, MFC 502 may represent aplurality of MFCs coupled via a common manifold or header to a commonoutlet, wherein MFC 502 as described below may represent the one MFC ofthe plurality of MFCs to be verified (i.e., the only MFC of theplurality of MFCs flowing gas during verification).

Process chamber 506 may be coupled to a flow path 508 coupled to massflow controller 502 via an isolation valve 510. Process chamber 506 maybe configured to receive one or more process chemistries via MFC 502 andto have a reduced-pressure chemical vapor deposition process, or areduced-pressure epitaxy process, or one or more deposition, oxidation,nitration, etching, polishing, cleaning, and/or lithography processesperformed therein.

Mass flow verification system 504 may have an inlet 512 and an outlet514. Inlet 512 may be coupled to MFC 502 via isolation valve 510. Massflow verification system 504 may be any one of mass flow verificationsystems 100, 200, or 300 described above.

In those embodiments where electronic device manufacturing system 500operates under a reduced-pressure application, mass flow verificationsystem 504 may be any one of mass flow verification systems 100, 200, or300. Mass flow verification system 504 may be coupled via outlet 514 toa system vacuum pump 516 of electronic device manufacturing system 500via an isolation valve 518. System vacuum pump 516 may also be coupledto process chamber 506 via isolation valve 518.

In those embodiments where electronic device manufacturing system 500operates under an atmospheric application, mass flow verification system504 may be mass flow verification system 100, 200, or 300 and the systemvacuum pump 516 may be excluded from electronic device manufacturingsystem 500.

The operation of electronic device manufacturing system 500 and/or massflow verification system 504 may be controlled by a controller such as,e.g., one of controllers 120, 220, or 320.

FIG. 6 illustrates a flowchart of a method 600 of verifying a MFC flowrate in accordance with one or more embodiments. Initially, a gas issupplied to a calibrated flow standard and flowed through a seriallyconnected control volume and a flow restrictor (602). The gas is floweduntil a steady state stabilized pressure is achieved in the controlvolume. Optionally, the pressure in the control volume can be boosted(604) to provide more range over which the decaying pressure can bemeasured. Next, the pressure is measured upstream of the flow restrictorin the control volume (606). The flow from the gas supply is terminatedand the gas pressure decay in the control volume is measured over time(608), and this data, along with the set point of the calibrated flowstandard, is used to compute the actual volume of the control volume(608). The calibrated control standard is replaced with a MFC to betested (UUT) and gas is flowed until a steady state stabilized pressureis achieved in the control volume (610). Optionally, the pressure in thecontrol volume can be boosted (612) to provide more range over which thedecaying pressure can be measured. The pressure in the control volume ismeasured (614), the flow from the gas supply is terminated, and the gaspressure decay in the control volume is measured over time based on thecomputed actual control volume (616). The set point of the MFC undertest is verified by comparing the set point of the MFC under test to theactual computed mass flow determined by measuring the pressure decaywith the tested MFC installed, where any difference is the error in theMFC (618). The MFC is calibrated to correct for the error determined inthe MFC (620).

The above process blocks of method 600 may be executed or performed inan order or sequence not limited to the order and sequence shown anddescribed. For example, in some embodiments, one process block may beperformed simultaneously with or after another process block. In someembodiments, a non-transitory computer-readable storage medium, such as,e.g., a removable storage disk, memory or device, may include computerreadable instructions stored thereon that are capable of being executedby processor, such as, e.g., controllers 120, 220, 320, to performprocess blocks 602-620 of method 600.

The foregoing description discloses only example embodiments of thedisclosure. Modifications of the above-disclosed assemblies, apparatus,systems, and methods may fall within the scope of the disclosure.Accordingly, while example embodiments of the disclosure have beendisclosed, it should be understood that other embodiments may fallwithin the scope of the disclosure, as defined by the following claims.

What is claimed is:
 1. An electronic device manufacturing system,comprising: a gas supply; a mass flow controller (MFC) coupled to thegas supply; an inlet coupled to the MFC; an outlet; a control volumeserially coupled to the inlet to receive a gas flow; a flow restrictorserially and directly coupled to the control volume and to the outlet; acontroller adapted to allow the gas supply to flow gas through thecontrol volume and the flow restrictor to achieve a stable pressure inthe control volume, terminate the gas flow from the gas supply, andmeasure a rate of pressure decay in the control volume over time; and aprocess chamber coupled to a flow path, wherein the flow path includesthe control volume and is coupled to the mass flow controller, theprocess chamber to receive one or more process chemistries via the massflow controller.
 2. The electronic device manufacturing system of claim1, further comprising a valve coupled between the inlet and the controlvolume, wherein the valve is operable by the controller to terminate thegas flow from the gas supply.
 3. The electronic device manufacturingsystem of claim 1, wherein the controller is to determine an error inthe MFC by comparing a set point of the MFC to an actual mass flowcalculated based on a volume of the control volume, wherein the volumeis determined based on the rate of pressure decay in the control volumeover time measured with a calibrated gas flow standard.
 4. Theelectronic device manufacturing system of claim 1, wherein the flowrestrictor is at least one of a drilled orifice flow restrictor or aporous media flow restrictor.
 5. The electronic device manufacturingsystem of claim 1, further comprising a valve coupled between thecontrol volume and the flow restrictor, the valve operable by thecontroller to cause pressure to build in the control volume.
 6. Theelectronic device manufacturing system of claim 1, further comprising asecond volume couplable to the control volume and operable by thecontroller to boost pressure in the control volume by supplying apressurized gas to the control volume.
 7. The electronic devicemanufacturing system of claim 6, further comprising: a first valve forcoupling the second volume to the inlet; and a second valve for couplingthe second volume to the control volume.
 8. The electronic devicemanufacturing system of claim 1, wherein the process chamber is toperform one or more of a reduced-pressure chemical vapor depositionprocess, a reduced-pressure epitaxy process, or at least one ofdeposition, oxidation, nitration, etching, polishing, cleaning, or alithography process performed within the process chamber.
 9. A method ofverifying a mass flow controller, the method comprising: causing a gasto flow from a gas supply through a calibrated flow standard, a controlvolume, and a flow restrictor at a stable pressure measured in thecontrol volume, wherein the flow restrictor is serially and directlycoupled to the control volume and to an outlet; terminating the gas flowfrom the gas supply; measuring a first rate of gas pressure decay in thecontrol volume; replacing the calibrated flow standard with the massflow controller; causing the gas to flow from the gas supply through themass flow controller, the control volume, and the flow restrictor at astable pressure measured in the control volume; terminating the gas flowfrom the gas supply; and measuring a second rate of gas pressure decayin the control volume for purposes of verifying the mass flowcontroller.
 10. The method of claim 9, further comprising determining anerror of the mass flow controller by: computing a volume of the controlvolume based on the first rate of gas pressure decay; using the computedvolume to determine an actual mass flow based on the second rate of gaspressure decay; and comparing the actual mass flow to a set point of themass flow controller.
 11. The method of claim 10, further comprisingcalibrating the mass flow controller based on the determined error ofthe mass flow controller.
 12. The method of claim 9, further comprisingincreasing the stable pressure in the control volume before measuringthe first and second rates of gas pressure decay.
 13. A non-transitorycomputer-readable storage medium on which computer readable instructionsare stored, wherein the computer readable instructions, when executed bya processor, cause the processor to perform the method of claim
 9. 14. Asystem comprising: an inlet coupled to a mass flow controller, which iscoupled to a gas supply; an outlet; a control volume serially coupled tothe inlet to receive a gas flow from the gas supply; a flow restrictorserially and directly coupled to the control volume and to the outlet;and a controller adapted to allow the gas supply to flow gas through thecontrol volume and the flow restrictor to achieve a stable pressure inthe control volume, terminate the gas flow from the gas supply, andmeasure a rate of pressure decay in the control volume over time toverify the mass flow controller.
 15. The system of claim 14, furthercomprising a valve coupled between the inlet and the control volume,wherein the valve is operable by the controller to terminate the gasflow from the gas supply.
 16. The system of claim 14, wherein thecontroller is further to determine an error in the mass flow controllerby comparing a set point of the mass flow controller to an actual massflow calculated based on a volume of the control volume, wherein thevolume is determined based on the rate of pressure decay in the controlvolume over time measured with a calibrated gas flow standard.
 17. Thesystem of claim 14, wherein the flow restrictor is at least one of adrilled orifice flow restrictor or a porous media flow restrictor. 18.The system of claim 14, further comprising a valve coupled between thecontrol volume and the flow restrictor, the valve operable by thecontroller to cause pressure to build in the control volume.
 19. Thesystem of claim 14, further comprising a second volume couplable to thecontrol volume and operable by the controller to boost pressure in thecontrol volume by supplying a pressurized gas to the control volume. 20.The system of claim 19, further comprising: a first valve for couplingthe second volume to the inlet; and a second valve for coupling thesecond volume to the control volume.